1. Field of the Invention
This invention is directed to processes for the concentration, recovery and at least partial purification of higher diamondoid components from petroleum feedstocks.
2. Background Information
The following publications and patents are provided as background and if cited herein may be identified by their superscript numbers:    1 Fort, Jr., et al., Adamantane: Consequences of the Diamondoid Structure, Chem. Rev 64, 277–300 (1964)    2 Sandia National Laboratories (2000), World 's First Diamond Micromachines Created at Sandia, Press Release, (2/22/2000) www.Sandia.gov.    3 Lin, et al., Natural Occurrence of Tetramantane (C22H28), Pentamantane (C26H32) and Hexamantane (C30H36) in a Deep Petroleum Reservoir, Fuel 74, (10):1512–1521 (1995)    4 Dahl, et al., Diamondoid Hydrocarbons as Indicators of Natural Oil Cracking, Nature, 54–57 (1999)    5 McKervey, Synthetic Approaches to Large Diamondoid Hydrocarbons, Tetrahedron 36, 971–992 (1980)    6 Chung et al., Recent Development in High-Energy Density Liquid Fuels, Energy and Fuels 13, 641–649 (1999)    7 Balaban et al., Systematic Classification and Nomenclature of Diamond Hydrocarbons-I, Tetrahedron 34, 3599–3606 (1978)    8 Handbook of Petroleum Refining Processes, Second Edition, Robert A. Myers, Editor, McGraw Hill (1997)            Chapters: 7.1 “MAK Moderate—Pressure Hydrocracking” by M. C. Hunter, et al.                    7.2 “Chevron Isocracking—Hydrocracking for Superior Fuel and Lubes Production” by Alan C. Bridge            7.3 “UOP Unicracking Process for Hydrocracking” by Mark Reno            8.1 “Chevron RDS/VRDS Hydrotreating” by David N. Brossard, and            8.4 “UOP RCD Unionfining Process” by Gregory J. Thompson                            9 Rollman et al, Adamantane for Petroleum with Zeolites, Abstracts, 210th ACS National Meeting, Chicago, Ill., Aug. 20–24, 1995—Fuel, pgs. 1012–1017    10 Petrov et al., Saturated Tricyclic C11-C13 Hydrocarbons From (two Soviet) Crude Oils, Neftekhimiya 13 N3, 345–351 (May-June 1973)    11 Wingert, G. C.—M.S. Analysis of Diamondoid Hydrocarbons in Smackover Petroleums, Fuel 71, 38 (January 1992)    12 J. Am. Chem. Soc. 114:10834–10843 (1992)    13 Kresge, et al., Nature 359:710 (1992)    14 U.S. Pat. No. 3,852,207    15 U.S. Pat. No. 4,347,121    16 U.S. Pat. No. 4,401,556    17 U.S. Pat. No. 4,534,852    18 U.S. Pat. No. 4,556,646    19 U.S. Pat. No. 4,820,402    20 U.S. Pat. No. 4,913,799    21 U.S. Pat. No. 4,956,747    22 U.S. Pat. No. 4,956,748    23 U.S. Pat. No. 4,956,749    24 U.S. Pat. No. 4,982,049    25 U.S. Pat. No. 5,019,665    26 U.S. Pat. No. 5,059,567    27 U.S. Pat. No. 5,073,530    28 U.S. Pat. No. 5,080,776    29 U.S. Pat. No. 5,114,563    30 U.S. Pat. No. 5,198,203    31 U.S. Pat. No. 5,246,689    32 U.S. Pat. No. 5,306,851    33 U.S. Pat. No. 5,334,368    34 U.S. Pat. No. 5,414,189    35 U.S. Pat. No. 5,439,860    36 U.S. Pat. No. 5,468,372    37 U.S. Pat. No. 5,498,812    38 U.S. Pat. No. 5,925,235    39 U.S. Pat. No. 6,013,239    40 U.S. Pat. No. 6,179,995    41 “Improved Ni—Mo HDN catalysts through increased dispersion and intrinsic activity of the active phase” Inoue, Yoshimasa; Uragami, Yuji; Takahashi, Yasuhito; Eijsbouts, Sonja. Nippon Ketjen Co., Ltd., Tokyo, Japan. Studies in Surface Science and Catalysis (1999), 121 Science and Technology in Catalysis (1998)
All of the above publications and patents are herein incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference in its entirety.
Diamondoids are cage-shaped hydrocarbon molecules possessing amazingly rigid structures that are superimposable fragments of the diamond crystal lattice. Adamantane, a ten-carbon molecule, is the smallest member of the diamondoid series, consisting of one diamond crystal subunit. Diamantane contains two face-fused diamond subunits and triamantane three. Adamantane and diamantane and to a lesser extent, triamantane, are well studied. They have been isolated from petroleum feedstocks and synthesized heretofore. The art has come to refer to adamantane, diamantane, triamantane and substituted analogs thereof as “lower diamondoids”. Tetramantane and larger diamondoids and substituted analogs, which exists as multiple isomers are referred as “higher diamondoids”. That nomenclature is used herein.
Until recently, the higher diamondoids were only minimally described. Lin, et al.3 reported the natural occurrence of tetramantane, pentamantane and hexamantane in deep petroleum reservoirs. However, these workers were only able to tentatively identify such compounds in ionized form as part of mass spectroscopy analyses.
Partridge, et al.25 disclosed a process for concentrating diamondoid-containing hydrocarbon solvents. This process involved three steps. The first was providing a solvent mixture made up of at least 50% by weight normal or slightly-branched C5–C30 paraffins having dissolved therein at least one diamondoid compound. In the second step, this mixture is contacted with a shape-selected catalyst in the presence of added hydrogen to convert at least a portion of the normal or slightly branched paraffins to lower-boiling aliplaties and to prevent the conversion of more than about 10% by weight of the diamondoid compounds. In the third step the lower-boiling aliplaties and the diamondoids are separated from one another.
Chen, et al.34 disclosed methods for isolating high purity lower diamondoid fractions and components. The disclosed methods involved distilling a diamondoid-containing feedstock into five overhead components. These overhead components included adamantane, diamantane and triamantane. Chen, et al. further recited that the pot material recovered after the distillation contained a major amount of substituted triamantane and minor amounts of tetramantane and pentamantane. Again, the Chen et al. identifications were speculative, with no isolations or definitive characterizations.
More recently, present co-inventors Dahl and Carlson filed a series of United States patent applications in which they described the isolation, identification and characterization of a large number of individual higher diamondoids ranging from all four possible tetramantanes through undecamantane.
See for example:
    42 U.S. Ser. No. 10/012,333, now U.S. Pat. No. 6,843,851, issued Jan. 18, 1005;    43 U.S. Ser. No. 10/012,334, now U.S. Pat. No. 6,828,469, issued Dec. 7, 2004;    44 U.S. Ser. No. 10/012,335, now U.S. Pat. No. 7,094,937, issued Aug. 22, 2006;    45 U.S. Ser. No. 10/012,336, now U.S. Pat. No. 6,743,290, issued Jun. 1, 2004;    46 U.S. Ser. No. 10/012,337, now U.S. Pat. No. 7,034,194, issued Apr. 25, 2006;    47 U.S. Ser. No. 10/012,545, now U.S. Pat. No. 6,815,569, issued Nov. 9, 2004;    48 U.S. Ser. No. 10/012,546, now U.S. Pat. No. 6,831,202, issued Dec. 14, 2004;    49 U.S. Ser. No. 10/012,704, now U.S. Pat. No. 6,812,370, issued Nov. 2, 2004;    50 U.S. Ser. No. 10/012,709, now U.S. Pat. No. 6,812,371, issued Nov. 2, 2004; and    51 U.S. Ser. No. 10/017,821, now U.S. Pat. No. 6,844,477, issued Jan. 18, 2005; all filed on Dec. 12, 2001; and    52 U.S. Ser. No. 10/046,486, filed Jan. 16, 2002, now U.S. Pat. No. 6,858,700, issued Feb. 22, 2005; and    53 U.S. Ser. No. 10/052,636 filed on Jan. 17, 2002, now U.S. Pat. No. 6,861,569, issued Mar. 1, 2005, and all incorporated herein by reference. These patent applications describe how the higher diamondoids were isolated from petroleum feedstocks such as deep reservoired oils and gas condensates. The concentrations of higher diamondoids in these feedstocks were reported to be quite low, generally in the parts per thousand to parts per billion range. In addition, the relative concentrations of the various higher diamondoids were found to decrease rapidly as the size of the diamondoids increased. The other components of the feedstocks included nondiamondoids including nondiamondoid hydrocarbons, sulfur-containing materials and metal-containing materials and lower diamondoids.
A variety of methods to concentrate and isolate the higher diamondoids were taught in the Dahl and Carlson patent filings. Fractionation procedures, both atmospheric and vacuum, were disclosed and isolated fractions enriched in one or more of the desired higher diamondoids relative to the distillation feedstock were described. Thermal treatment (“pyrolysis”) was taught as a desirable process step. In this step the feedstock or a feedstock distillation fraction was heated in a Parr reactor at about 400–500° C. for up to about 20 hours. This pyrolysis step preferentially broke down the nondiamondoid materials to lower molecular weight materials such as gases which were easily removed. The diamondoilds, being more stable, were pyrolyzed to a lesser extent. This increased the concentration of the higher diamondoids in the pyrolysis product.
While the pyrolysis step has proven advantageous in its breaking down of nondiamondoid materials, typically it is time consuming and often appears to reduce ultimate yields of the desired higher diamondoids. Accordingly, there is a need for an improved process to assist in the concentration and isolation and recovery of the higher diamondoids.
As will be discussed below, the present invention employs hydroprocessing to treat higher-diamondoid-containing feedstocks and thus to facilitate the separation of higher diamondoids from nondiamondoids. Hydroprocessing is used in many petroleum processing settings. It involves contacting a petroleum feedstock with hydrogen at elevated temperatures, most often with a solid phase catalyst. Sub-categories of hydroprocessing include “hydrotreating” and “hydrocracking”. “Hydrotreating” is a hydroprocess carried out under conditions to react or remove contaminants from the feedstocks. Such contaminants include sulfur-containing contaminants (in which case the process may be referred to as “hydrodesulfurization”), nitrogen-containing contaminants (“hydrodenitrification”), and metals, which can be in the form of organometallic compounds, (“hydrodemetallation”). Hydrotreating also can include hydrogenation of olefinic and aromatic unsaturation.
In “hydrocracking”, petroleum feedstock is contacted with a catalyst at elevated temperatures in the presence of hydrogen to crack or otherwise convert undesired components to more desirable species or to preferentially break down undesired species. The first modern hydrocracking operation was placed on stream in the 1950's by the Standard Oil Company of California. Since the 1960's, hydrocracking has been used in many settings. These include the formation of liquefied petroleum gas (LPG) from naptha feedstocks, the preparation of high quality distillate fuels from gas oils and other heavy stocks, the formation of jet and diesel fuels from vacuum gas oils and the processing of heavy feedstreams such as residuums to fuels and lubricating oils.
In many settings, hydroprocessing involves a combination of several of these reactions taking place simultaneously in the same reaction zone or sequentially in serial zones. As conditions such as temperature, pressure, space velocity and catalysts are altered, the relative impact of the various reactions can change.